Sitting for more than three hours a day can cut two years off a person’s life expectancy, even if he or she exercises regularly, a new study finds. Watching TV for more than two hours a day can shorten life expectancy even further, by another 1.4 years.

The findings suggest that when it comes to gleaning health benefits from physical activity, it may not be enough just to get the recommended amount of daily exercise — the government advises about a half-hour of moderate activity a day for adults. But what about the other 23.5 hours of every day? Researchers say it’s important not to spend it sedentary or sitting.

In the same way that both pushing the gas and hitting the brake can adjust the speed of your car, researchers say that physical activity and sedentary behavior independently affect your health and life expectancy. Whether “you’re physically active and meet the exercise guidelines, or if you’re not active,” says Peter Katzmarzyk, professor of epidemiology at Pennington Biomedical Research Center and lead author of the new paper published in the online journal BMJ Open, “sitting is bad.”

Katzmarzyk’s isn’t the first study to document the ill effects of sedentary behavior. An Australian study published last August found that people who watched an average of six hours of TV a day lived 4.8 years less than those who didn’t watch any television; what’s more, every hour of TV that people watched after age 25 was associated with a 22-minute reduction in their life expectancy.

The current analysis differed from previous research in that it took a broader look, calculating the cumulative effect on overall life expectancy of a sedentary population. Recent surveys show that worldwide people spend about 300 minutes, or 20% of their day, sitting; many people spend much longer. Shaving at least a couple of hours off that time — by turning off the computer, TV or other digital media, for example — could add years to life expectancy, the new study suggests.

To gauge the effect of being sedentary, Katzmarzyk and his colleagues pooled data from five studies that asked participants about their sedentary habits, including how much time they spent sitting, watching TV or using the computer screen. The researchers folded in the mortality risk associated with sedentary behavior, and then calculated how many years of life would be gained if these risk factors were removed from life expectancy calculations.

Sitting, it turns out, can shorten life expectancy almost as much as smoking can, which highlights just how damaging inactivity can be, particularly for the heart. “What the results mean is that we got everyone in the U.S. to sit less, our population life expectancy would be two years higher, so instead of living to 78.5, we would be expected to live to 80.5 years old,” says Katzmarzyk. “That’s a really big deal.”

But getting people to spend less time in their chairs isn’t easy, especially for those who work sedentary jobs at an office desk. Even people who meet the government’s exercise guidelines may spend most of the rest of their days parked on a sofa or chair.

You can start by getting up from your chair intermittently at work. Take walks around the hall in your office or try holding walking meetings instead of sitting around a table. Get up to chat with your colleague instead of sending an email. Standing doesn’t take the place of exercise, but it should replace a good chunk of time you spend in your chair. The key is to spend as little time as possible sitting down.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.